The U.S.-led coalition targeting the Islamic State group in Syria and Iraq said Thursday its airstrikes have killed 801 civilians since late 2014.

The figures came in the coalition's latest monthly statement about its investigations into reports of possible civilian casualties resulting from the strikes.

In October, the coalition says it investigated 64 such reports, of which five were deemed credible and resulted in 15 deaths. Another 695 reports were still open.

"We continue to hold ourselves accountable for actions that may have caused unintentional injury or death to civilians," the statement said. "We take all reports of civilian casualties seriously and assess all reports as thoroughly as possible."

Outside groups say the bombing campaign that began in August 2014 in Iraq and a month later in Syria has killed far more civilians than the coalition has reported.

Watchdog group Airwars estimates that as of the end of October the coalition airstrikes killed at least 5,961 civilians, and that the number could top 9,000. Its figures include at least 1,504 deaths in Iraq and 3,487 in Syria.

The Syrian Observatory for Human Rights said in late October it had documented 2,910 civilian deaths that resulted from coalition airstrikes in Syria.

The pace of airstrikes increased after U.S. President Donald Trump took office in late January. In December, according to coalition data, there were an average of about 16 airstrikes per day combined in Iraq and Syria. That number jumped to 25 per day in January and reached a peak of more than 50 strikes per day in August and September.

Those increases came along with supporting major operations to retake control of areas from Islamic State fighters, including Mosul in Iraq and the group's de facto capital in Raqqa, Syria.

Since the fall of Raqqa in mid-October, the number of strikes has plummeted, and November has seen one of the lowest number of strikes in the entire campaign.